1. Technical Field
The present invention relates to a semiconductor wafer, a method of producing a semiconductor wafer, and an electronic device.
2. Related Art
In recent years, electronic devices have achieved increasingly higher integration. Thus, a method has been proposed that forms a heterojunction bipolar transistor (HBT) and a field-effect transistor (FET) on the same wafer. IEDM Tech. Dig., 1992, p. 91 discloses that the emitter layer of an HBT may be used as the channel layer of an FET. IEDM Tech. Dig., 1989, p. 389 discloses that semiconductors used to form an AlGaAs/GaAs-based HBT may be stacked on semiconductors used to form a high electron mobility transistor (HEMT).
In a highly integrated electronic device, each electronic element may exhibit low performance since a plurality of semiconductor devices formed on the same wafer affect each other. For example, the performance of an HBT is improved preferably by increasing the conductivity of the collector by forming a subcollector layer having more impurities implanted therein. As the concentration of impurity atoms implanted in a semiconductor layer increases, however, the crystal structure of the semiconductor layer becomes unstable and crystal defects may be induced in the semiconductor layer. The defects may propagate into other semiconductor layers and grow therein.
For example, as the concentration of impurity atoms increases in the subcollector layer of a HBT, resulting crystal defects propagate into an FET, which is formed below the HBT, and degrade the performance of the FET. In light of the above, an object of the innovations herein related to the present invention is to provide a semiconductor wafer that can be used to form high-performance transistors by increasing the concentration of impurity atoms in a semiconductor layer formed in the semiconductor wafer with it being possible to reduce the crystal defects that may propagate into other semiconductor layers formed in the same semiconductor wafer.